The Keystone Symposia is a one of a kind meeting that focuses on multicellular eukaryotic parasites that are a major cause of morbidity in the world. This is an exciting time for the field of helminth host-parasite co-evolution. Advances in molecular and cellular biology of helminth parasite interactions with their hosts are being and are expected to accelerate as the genomic sequence of Schistosoma mansoni, S. japonicum and Brugia malayi will each be at 9X coverage and more than 200,000 ESTs for Schistosoma and over 200,000 ESTs for nematode species will be available during 2004. A renaissance of approach with studies on the transcrtptome and proteome and of technology and tools, such as gene transfers, gene knock-outs and RNA interference is underway. These tools, the manipulations and hypotheses they will allow, will be the topics for this unique conference. By the year 2005 the fruits of the new information and technological advances will be available. The Conference which combines broad areas of helminth research ranging from basic science such as developmental biology, signal transduction, and functional genomics translated to the applied aspects such as targets for vaccine and drug design and drug resistance has as its theme how host and parasite molecules each contribute to host-parasite co-evolution. It is expected that the conference will promote collaboration among researchers with the goal of identifying new targets for the development of drugs, vaccines, and diagnostic tests, by providing the biological and informatic resources and tools for their rapid characterization and analysis, by analyzing the biological basis of host-parasite interactions and by attracting new young talent which is essential for the vitality of the field. Certainly there are fascinating scientific questions waiting to be answered about helminths. Some of those questions have as their central theme the very nature of parasitism.